Patent GB-1457116-A (GB)
Title: Method and apparatus for changing the disposition or position of a beam or point
IPC: G05D3/14
Filed: 1973-11-30
Abstract: 1457116 Automatic control; optical apparatus FRANCE ARMED FORCES MINISTER OF 30 Nov 1973 [30 Nov 1972] 55750/73 Headings G2N and G2U [Also in Division H4A] The Specification describes apparatus for deflecting an optical beam the radiation in which may be infrared, visible, ultraviolet, or ultra high frequency radio waves. The beam is adjusted in the direction by which it is ultimately directed into a telescope or other optical system and may find application in a firing control installation in which the apparatus according to the invention receives information from a computer (not shown) regarding 2-D coordinates of a wanted position corresponding to a predetermined beam direction of the beam entering the apparatus, which is associated with a servocontrol follow-up system whereby the deflecting beam path in relation to the axis of a telescope or optical system provided with the apparatus, is brought into an orientation such that the barrel to which the telescope is fixed is correctly aimed when the target appears on the cross-hairs of the telescope Co-ordinates α c  and # c  of the predetermined beam direction having been supplied, the control system rotates a pair of axially cylindrical wedge-shaped prisms mounted in the apparatus to change the deflected path from an initial orientation to the wanted orientation, e.g. α m , # m . The sense of rotation of each prism movement is determined by the polarities of the expressions (α+#) c  - (α+#) m  - #1 and (# - α) c  - (# - α) m  - #2 The sense of rotation of the first prism depends on the polarity of #1 and of the second prism on #2. As described, the deflector apparatus, Fig. 5 deflects an off-axis optical beam (which may be visible: ultraviolet infrared, or ultra high frequency radiation) on to the axis XX' of the deflector by means of individually driven rotatable prisms 11, 11a. Each prism is a cylindrical section coaxial with XX'-and has truncated optical plane faces which converge towards a plane perpendicular to XX' and may further be provided with a flint glass and a crown glass element to produce achromatism in the visible and infrared ranges. The prisms, mounted in rings 31, 31a rotatable on bearings 32, 32a respectively are rotated by servomotors 10 which each comprise a stator 34 fitted in frame 33 and a rotor 35 fixedly mounted on ring 31. The image of a graduated scale is projected into the deflected beam path from light entering window 46, which is focused to infinity by lens system 47 and is reflected into the beam path by semitransparent plate 45. The prism position sensors 12, 12a comprise potentiometers, having annular resistive tracks 37 having sine wave variation. Sliders, of which two are provided to produce sine and cosine signals are fitted at quadrature on rings 31, 31a and provide signals 13, 14 in Fig. 2 corresponding to sin #, and cos #, resp. for prism 11; prism 11a similarly having detection outputs sin # 2 , cos # 2 . Signals 13, 14 provide part of the information to generate error signal #* 1  which drives servomotor 10; error signal #* 2  being derived similarly to drive servomotor 10a. Signal 13 is passed through amplifier 15 having a gain -#2d 1 . Error signal generator 16, receiving input position signals corresponding to α c  and # c  produces an output signal # 1  = (α c  + # c ) - #2 (d 1  sin # 1  - d 2  cos # 2 ). The signal representing cos # 2  from detector 12a is passed through an amplifier 15a having a gain #2d 2 . to provide the fourth signal required for the error signal generator 16. To avoid closed loop instability in the control system, correcting circuit 20, which may be an integrator-differentiator, supplies a phase advance of 55 degrees maximum, the output #* 1  is fed into a sign determining circuit 22 which generates a constant signal dependent on the polarity of #* 1 . This signal drives servomotor 10. A similar circuit derives a signal # 2  where # 2  = (# c  - α c ) - #2 (d 1  cos # 1  + d 2  sin # 2 ) to drive motor 10a which actuates prism 11a. In a further embodiment, inherent oscillations in the above system may be removed with an accompanied reduction in accuracy by pseudo-linear control circuit which uses a comparison between each error signal and two triangular waveforms, Fig. 4, (not shown) having a period greater than the servomotor time constant.